A. Field of the Invention
The present invention relates to a power controller, in particular, to a power controller in which a power detector, instead of a power coupler, is used for detecting the output power from each stage amplifier so as to effectively control the power and efficiency of each stage amplifier.
B. Description of the Related Art
FIG. 1 is a block diagram showing a conventional power control system. The symbol 100 refers to a GSM power controller. The function of the power controller 100 is to amplify the power of the radio frequency input signal that is emitted through an antenna 190. The power controller 100 is suitable for the power control system of the mobile phone. Referring to FIG. 1, the conventional power controller 100 includes a driver stage amplifier 110, an inter stage amplifier 120, a power stage amplifier 130, and matching circuits 140, 141, and 142 for each stage amplifier. In addition, in order to let each stage amplifier operate at a proper operating environment, the power controller 100 further includes two DC bias and analog power control circuits 150 and 151. The control circuit 150 receives a first control signal APC1 which is used for controlling the driver stage amplifier 110 and the inter stage amplifier 120. On the other hand, the control circuit 151 receives a second control signal APC2 which is used for controlling the power stage amplifier 130.
As shown in FIG. 1, the antenna 190 is used for emitting the radio frequency output signal of the power controller 100 in the power control system. At the same time, a power coupler 180 and a power detecting unit 170 are used for detecting the magnitude of the power of the radio frequency output signal. The power detecting unit 170 generates a control signal APC according to the magnitude of the output power. The control signal APC is inputted to the power controller 100 as signals APC1 and APC2, thereby controlling the operating voltage of each stage of the power controller 100.
Since the power of the output signal of the power controller 100 is relatively high, the power loss after the output signal passed through the power coupler 180 is also relatively high. Thus, a lot of energy may be wasted. Furthermore, since the output power at the last stage is close to the saturated region, it is difficult for the power coupler to correctly detect and control the magnitude of the power. On the other hand, there may be a problem of impedance mismatching caused by the high power loss. Also, the size of the power coupler 180 makes it very difficult for the device using the control system to be reduced in size. Moreover, since the control system only provides an APC signal to the control circuits 150 and 151 of the power controller 100, even though the amplifier possesses high efficiency at high power output, the amplifier cannot possesses high efficiency at low power output. Therefore, the energy is also wasted.